{	15 January 2011. Individual Olympiad. Problem set: http://neerc.ifmo.ru/school/io/archive/20110115/problems-individual-20110115.pdf
	Problem A
	Points: 100	
}

uses SysUtils;
var n,i:integer; s:string; res:int64;
begin
reset(input,'weiter.in');
rewrite(output,'weiter.out');
readln(n);
readln(s);
if n<length(s) then writeln('Impossible') else begin
  RES:=0;
  for i:=1 to length(s) do inc(res,ord(s[i])-96);
  writeln(res);
end;
end.
 